1. Field of the Invention
This invention relates to foam delivery systems for fire fighting use.
2. Description of the Prior Art
The addition of foaming agents to fire fighting water as a fire suppression agent has been recognized as early as the 1870's when the first such use was reported to have been patented in England. Since then, through the years, further advances have been made. These advances have included better understanding of the function of the foaming agent, the types of delivery systems and most significantly, the foam:water ratio for particular fire applications.
For many years, Class A type foams of the A-FFF type have never been used to combat fuel fires such as JP4 jet fuel, gasoline and diesel fuels. More recently, Class A foams, such as the agents sold under the trademark Sylvex of the Ansul company, have been found to increase the fire suppression efficiency of water by three to five times when used on both wildland and Class A structure fires. This recognition has greatly expanded the utility and usage of foam in fire fighting.
In the past, a fairly standard foam:water ratio of 6:94 was used and apparatus capable of maintaining such a ratio at various water flow rates was disclosed in a number of patents, such as 4,064,891 to Eberhardt and 4,448,256 to Eberhardt, et al. The '891 patent to Eberhardt discloses a balanced pressure valve. The '256 patent to Eberhardt, et al employs a positive displacement gear pump to maintain the standard ratio despite changes in flow rates.
More recently it has been recognized that foam:water ratios of 3:97 over flow rate variations of from 20 GPM to 1,000 GPM are needed and more complex proportioning valves such a shuttle type systems are illustrated by U.S. Pat. No. 4,633,895, also to Eberhardt.
With further development of foam suppression fire fighting, it has become apparent that foam:water ratios as low as 0.2:99.8 may be needed and precise proportioning at 0.2% increments up to a 1:99 ratio can be important in various applications.
The tremendous reduction in the ratio of foam to water with effective or enhanced effectiveness has several important results. First, existing foam handling and proportioning systems are incapable of such precise proportioning. One reason is that they are almost universally of an eductor or vacuum operated, if self powered, or subject to the variations of portable electrical power supplies. Secondly, the logistics of foam supply are greatly simplified because of the greatly reduced quantities used. In the case of airborne applications, such as helicopter or fixed wing air drops, the use of foam suppression is much more practical. Still remains the need for a simple, light-weight, self-powered foam supply and proportioning system.